This invention relates to optical power limiters and, more particularly, to optical power limiters for detector circuits which may encompass a broad spectral bandwidth including infrared radiation.
Detector circuits are often used in situations in which an overload may occur causing the detector to be damaged and become unusable. For example, infrared detectors are often able to operate in ranges in which the amount of power to be detected is unknown. They are quite able to cope with power up to approximately 10.sup.7 watts/cm.sup.2. However, if they encounter infrared signals over a threshold of approximately 10.sup.8 watts/cm.sup.2 the detector unit may well be saturated with an undesirably long recovery time, damaged, or destroyed. It is not believed that the prior art has provided any convenient solution to this problem.
One of the difficulties with solving the power overload problem is that the time necessary for reaction to potential overloads must be very short in order to protect the detector circuitry; consequently, normal feedback circuitry operating off the response of the detector circuitry does not operate rapidly enough in some situations to accomplish a power reduction before damage has been done to the detector. Thus, the limiter, in order to react most rapidly should assess the power of the infrared beam directly. This form of sensitivity is unusual in power limiters.
Another difficulty in providing a power limiter for infrared detectors is that such detectors often must operate over quite broad bandwidths. Consequently, the power limiting arrangements must also operate over similar broad bandwidths.
It is, therefore, a purpose of this invention to provide a power limiter for protecting detectors over a broad bandwidth.
It is another purpose of this invention to increase the speed of operation of power limiters.
An additional purpose of this invention is to provide a broad-band power limiter for infrared detectors.